This invention relates to polyurethanes and more particularly to an improved process for preparing polyurethanes and polyester polyurethanes and to heat curable polyester polyurethane producing compositions.
Over the past 25 years, the production of polyurethanes for industrial use and for use in the manufacture of market products has increased manyfold. Polyurethanes are conventionally maufactured by reacting polyisocyanates with polyether or polyester polyol compounds because of the low cost and high reactivity of these compounds. However, great care must be exercised by those handling isocyanates because of their extremely high toxicity. Because of the inherent hazards of handling isocyanates, continuing research for alternate methods of preparing polyurethanes which are competitive costwise with the conventional isocyanate-polyester polyol processes, and which are relatively free of safety hazards are constantly being sought.
British Pat. No. 944,310, published Dec. 11, 1963, discloses a method of producing certain polyurethanes by reacting dicarbamates with polyhydric alcohols in the presence of an ester interchange catalyst at temperatures of 150.degree. to 210.degree.C. U.S. Pat. No. 3,676,402, issued July 11, 1972, discloses the deblocking of blocked isocyanates followed by reaction with polyhydric compounds in the presence of stannoxane catalysts to form polyurethanes.
An improved method has now been discovered for preparing polyurethanes and polyester-polyurethanes without the necessity of using highly toxic isocyanates. Storage stable compositions have also been discovered which can be easily heat cured to valuable polyester polyurethane products.
Accordingly, it is an object of the invention to present an improved process for preparing polyurethanes and polyester polyurethanes.
It is another object of the invention to present a process for preparing polyurethanes which avoids the necessity of handling highly toxic isocyanates.
It is another object of the invention to present an improved process for preparing substantially linear high molecular weight polyurethanes and polyester polyurethanes.
It is another object of the invention to present a method of preparing polyurethanes from difunctional carbamates without the necessity of resorting to high reaction temperatures.
It is another object of the invention to present heat curable polyester polyurethane-producing compositions which are storage stable at ordinary room temperatures.
These and other objects of the invention will become readily apparent rom the description and examples of the invention which follow.